Repeated daily exposures of rhesus monkeys by operant conditioning technique to lights 2 to 3 log units below the gross damage threshold produce irreversible loss of blue cone response and loss of green cone response lasting from 18 to 40 days. Retinal sections of the eyes of the "blue-blinded" monkeys show swollen pigment epithelium and cone damage which ranges from swelling of mitochondria and axonal processes to total degeneration. In comparing the exposed with the unexposed eyes there also appears to be cones completely missing in vertical 1 micron thick retinal sections in the parafoveal region, which could, with further verification, lead to mapping the distribution across the retina of blue-sensitive receptors. It is proposed to continue this research with: (a) parametric studies of the wavelength-intensity-duration relationships for producing the effect, (b) further attempts to produce comparable changes with red lights, (c) histology of retinas exposed to green lights, (d) attempts to further verify and quantify the distribution of missing cones (e) ultrastructural studies, (f) the application of new techniques for measuring spectral sensitivity as a function of position across the central 18 degrees of the macula of performing rhesus.